As the nation struggled to understand what drove a Houston mother last June to drown her five children in the family's bathtub, the phones began ringing in the offices of the UCLA Pregnancy and Postpartum Mood Disorders Project.

Between calls from media seeking instant answers from experts came heartbreaking questions from anxious patients, agonized women already diagnosed with postpartum depression: Could it happen to them? Could their illness push them over the edge and make them kill their own babies?

While the tragic story of Andrea Yates continues to unfold - with questions arising about her past treatment for postpartum depression - physician Victoria Hendrick, director of the UCLA program, has been urgently pushing one salient point: Postpartum depression (PPD), which is experienced by roughly 2% of all new mothers, is most likely not the devastating trigger that clicked in the mind of Yates, sending her on a killing spree.

"Women who experience PPD are not violent," Hendrick stressed. "It's very unlikely that what Andrea Yates did was the result of that. It's been revealed that she was being treated for some kind of psychotic illness. There is a rare disorder called postpartum psychosis that affects one out of every 1,000 new mothers. That is a real danger for children."

Women in the grips of postpartum psychosis are typically delusional. They suffer from hallucinations that cast their babies in an evil light or as already dead, the physician explained. "The worst are the command hallucinations," Hendrick noted, "when they hear voices telling them to do something to the baby. It can create very dangerous situations."

Postpartum psychosis is one of several treatable postpartum disorders that include short-term baby blues (which can affect between 50-80% of new mothers and is linked to sudden changes in hormonal levels) and PPD, the most common type.

Recent research on PPD points to a link with psychosocial factors.

"For example, women with a history of depression run a 25% chance of getting this, while those who have never been depressed face only a 5% chance," Hendrick said. Marital conflict, lack of social support and caring for another child under 2 years old also pose risks.

In Los Angeles, many women going through emotional difficulties during pregnancy or after delivery have been receiving treatment through the project Hendrick directs through the Neuropsychiatric Institute. Most have been helped with antidepressants or a combination of anti- depressants, psychotherapy, support groups and counseling. A full 96% of the women have responded successfully.

"Virtually everybody gets better," she said.

And for women with postpartum disorders who have been reluctant to take antidepressants because they want to breastfeed, there's more good news: Studies by Hendrick and other researchers at Emory and Harvard universities show that the newer antidepressants, known as selective serotonin reuptake inhibitors, such as Paxil, should not impair breastfeeding.

"The amount that babies get in breast milk is very small," Hendrick said. "These exposures don't appear to affect the baby. We've been tracking these children up to two years postpartum and have found no reason for concern."

For more information on PPD, call UCLA's Pregnancy and Postpartum Mood Disorders Program at (310) 794-9913. To be put in touch with others who have coped with PPD, call Santa Barbara-based Postpartum Support International at (805) 967-7636.